There is conventionally proposed a variable toll collection system that a toll for a toll road is computed according to an average traveling speed during traveling the toll road (refer to Patent Document 1). In this system, a traveling start time or a traveling end time is detected by a road-vehicle communications between an in-vehicle unit and an entrance toll booth or an exit toll booth when a vehicle passes through the entrance toll booth or the exit toll booth, respectively. A necessary time period or a toll-road use time period for traveling the toll road is thereby computed based on the traveling start time and the traveling end time. Further, a traveled distance on the toll road is obtained based on a distance from the entrance toll booth to the exit toll booth. Then, based on the traveled distance and the necessary time period, an average traveling speed is computed. It is thereby designed that as the average traveling speed decreases, a toll to be paid decreases.
Patent Document 1: JP-2001-338316 A
As described above, by using a road-vehicle communications, a vehicle automatically pays a toll when the vehicle passes through a toll booth on a toll road without stopping. This system is in practical use as the Electronic Toll Collection System (ETC). With respect to a vehicle having an ETC in-vehicle unit associated with the ETC, it is investigated that a toll be partially paid back based on a used distance in some metropolitan toll roads such as the Metropolitan Expressway and the Hanshin Expressway adopting a constant-amount toll. That is, with respect to a vehicle having an ETC in-vehicle unit that pays a constant toll at an entrance toll booth or gate, the toll is partially paid back based on a toll-road used distance.
In this used-distance payment system, a used distance needs confirming, so that it is studied that communications devices (exit ETC devices) are installed at exits of the toll roads for confirming a traveled distance.
However, installation of an exit ETC device needs additional costs; further, for instance, in the Metropolitan Expressway that includes a loop line, only confirming the traveled distance at the exit does not accurately confirm, for instance, the used distance of a vehicle that circles the loop line in more than one cycle.
To solve this, another communications device may be installed at a branching point of the loop line for confirming that a vehicle passes through the branching point. However, this communications device is needed for each of the branching points, so that installing of a roadside infrastructure needs much more cost than installing only exit ETC devices.